I. Field
The following description relates generally to wireless communications, and more particularly to methods and apparatus for Radio Link Control (RLC) layer re-transmission schemes and their selection.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, . . . ). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP LTE systems, orthogonal frequency division multiplexing (OFDM), localized frequency division multiplexing (LFDM), orthogonal frequency division multiple access (OFDMA) systems, and the like.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into Ns independent channels, which are also referred to as spatial channels, where NS≦min {NT, NR}. Each of the Ns independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beam forming gain on the forward link when multiple antennas are available at the access point.
In a wireless communication system, a Node B (or base station) may transmit data to a user equipment (UE) on the downlink and/or receive data from the UE on the uplink The downlink (or forward link) refers to the communication link from the Node B to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the Node B. The Node B may also send control information (e.g., assignments of system resources) to the UE. Similarly, the UE may send control information to the Node B to support data transmission on the downlink and/or for other purposes.
Previously protocol data units (PDUs) have been transmitted in order. Now a hybrid automatic retransmission request (HARQ) layer uses multiple transmission paths and the PDUs are not always transmitted in order. Additionally, the HARQ layer and the RLC layer do not directly talk to each other. The RLC layer will wish to send protocol data units (PDUs). The HARQ layer will actually transmit the PDUs via multiple channels. However, the RLC layer does not currently with multiple paths know that all the PDUs were actually received. Therefore, there is a need for the RLC layer to know when to re-transmit PDUs.